The research on vacuum isothermal bloom for powder metallurgy V-5Cr-5Ti alloy guiding by the constitutive models and the error analysis

Abstract For studying the vacuum isothermal cogging technology for V-5Cr-5Ti alloy, the isothermal hot compression tests are conducted in the deformation temperature ranging from 1150 °C(1423 K) to 1400 °C(1673 K) with an interval of 50 °C, strain rate ranging from 0.001 to 1 s−1 and height reductions of 55% on a computer controlled thermal simulation machine. The three kinds of constitutive equations of V-5Cr-5Ti alloy are deduced based on the true stress–strain curves. The analysis is carried out for the error for constitutive models and the optimum deformation condition. Isothermal hot cogging in vacuum is carried out guiding by the constitutive models and the optimum deformation conditions. Warm rolling is adopted for sheet manufacture of the cogging billet. The test results show that strain-compensated Arrhenius constitutive model is the most accurate and modified Johnson Cook constitutive model is the most efficient among them; by the solution steps, microstructure with metallographic and EBSD technology and other factors, the error reasons generated at lower strain rate of 0.001 s−1 and 0.01 s−1 in the modified Johnson-Cook and Zerilli-Armstrong models are explicit to some extent; the optimum deformation condition is at the temperature of 1250–1400 °C and the strain rate is 0.001–0.02 s−1, which are determined through strain rate sensitivity coefficients(m), deformation activation energy(Q) and the processing map; the mechanical properties of the sheet by warm rolling are the yield of 400 MPa, the tensile strength of 535 MPa and the elongation rate of 35%. And the material utilization rate is high up to 90%.